Science of the Total Environment 609 (2017) 484–496

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Science of the Total Environment

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Response of stream benthic macroinvertebrates to current water management in Alpine catchments massively developed for hydropower

Silvia Quadroni a,⁎, Giuseppe Crosa a, Gaetano Gentili b, Paolo Espa c a Department of Theoretical and Applied Sciences, University of Insubria, Via JH Dunant 3, Varese 21100, Italy b Graia s.r.l., Via Repubblica 1, Varano Borghi, VA 21020, Italy c Department of Science and High Technology, University of Insubria, Via GB Vico 46, Varese 21100, Italy

HIGHLIGHTS GRAPHICAL ABSTRACT

• Minimum flows are currently imple- mented in the study area as environ- mental flows. • 5-years monitoring of streamflow and benthos was performed at 20 regulated reaches. • Differences of benthic communities were found at sites with different flow patterns. • According to the current Italian stan- dards, stream quality was on average good/high.

article info abstract

Article history: The present work focuses on evaluating the ecological effects of hydropower-induced streamflow alteration Received 31 March 2017 within four catchments in the central Italian Alps. Downstream from the water diversions, minimum flows are Received in revised form 11 July 2017 released as an environmental protection measure, ranging approximately from 5 to 10% of the mean annual nat- Accepted 11 July 2017 ural flow estimated at the intake section. Benthic macroinvertebrates as well as daily averaged streamflow were Available online xxxx monitored for five years at twenty regulated stream reaches, and possible relationships between benthos-based Editor: D. Barcelo stream quality metrics and environmental variables were investigated. Despite the non-negligible inter-site differences in basic streamflow metrics, benthic macroinvertebrate commu- Keywords: nities were generally dominated by few highly resilient taxa. The highest level of diversity was detected at sites Alpine catchment where upstream minimum flow exceedance is higher and further anthropogenic pressures (other than hydro- Biomonitoring power) are lower. However, according to the current Italian normative index, the ecological quality was good/ Environmental flow high on average at all of the investigated reaches, thus complying the Water Framework Directive standards. fl Minimum ow © 2017 Elsevier B.V. All rights reserved. Water management Water Framework Directive

1. Introduction snowfields, combined with altered precipitation regimes, are driving shifts in hydrology and thus in biology (Hotaling et al., 2017). Frequent- The effects of climate change on the environment is a major topic in ly, these changes are superimposed upon anthropogenic hydrological current ecological research. In Alpine catchments, receding glaciers and alterations. Most of the Alpine streams are massively exploited for hy- dropower generation and their flow regime is highly regulated ⁎ Corresponding author. (Schinegger et al., 2012; Bruno et al., 2013; Premstaller et al., 2017). E-mail address: [email protected] (S. Quadroni). Due to the steep slopes typical of the Alpine areas, hydropower systems

http://dx.doi.org/10.1016/j.scitotenv.2017.07.099 0048-9697/© 2017 Elsevier B.V. All rights reserved. S. Quadroni et al. / Science of the Total Environment 609 (2017) 484–496 485 often induce severe water depletion in long river reaches, also in case of We tested the basic hypothesis that stream reaches characterized by run-of-the-river projects (Lazzaro and Botter, 2015), which are widely a relatively minor streamflow alteration would provide a better habitat, recognized to impact river environments to a much smaller extent supporting richer and more diverse benthic macroinvertebrate commu- than reservoir systems (Bilotta et al., 2017). nities. As a proxy of hydrological alteration in a regulated stream reach, Despite the huge efforts of the scientific community to define proper we adopted an index relating the actual streamflow and the MF released streamflow standards in regulated rivers, ecohydrological science still at the upstream diversion structure. needs future investigation to provide the necessary knowledge and tools for policy development and distribution of sustainable water alloca- tion (Acreman et al., 2014). Moreover, the management of flow releases 2. Materials and methods to better meet both human and ecosystem needs is a complex societal challenge involving not only scientists but also water resources managers, 2.1. Study area policy makers and the public (Acreman et al., 2014; Acreman, 2016). The Water Framework Directive (WFD, 2000/60/EC) is the main leg- Our investigation was carried out in the central Italian Alps, in the islative reference for the European Union (EU) countries regarding catchments of Mera, Adda, Oglio, and Caffaro rivers (Fig. 1). water-related issues. Despite not using the term environmental flow The Adda and Mera rivers are the main tributaries of Lake Como, (hereafter e-flow) explicitly, the WFD requires the achievement of with drainage areas of 2600 and 760 km2, respectively. Both catchments “good ecological status” (GES, i.e. a slight deviation from a type- are transboundary, with Swiss quotas of approximately 480 and specific reference condition) for all water bodies in the EU context. 100 km2. The Oglio (1400 km2 basin area) and the Caffaro (140 km2 Within the WFD, it is accepted that ecologically appropriate hydrologi- basin area) drain into the Iseo and Idro lakes, respectively. cal regimes are necessary to meet GES (Acreman and Ferguson, 2010) These catchments share common traits, typical of Alpine areas. Max- and a relevant guidance document provides detailed recommendations imum elevations range from 3000 to 4000 m asl (except for the Caffaro for considering e-flow in the WFD implementation (WFD CIS, 2015). basin, where maximum elevation is 2500 m asl). Water surface eleva- This document prompts the EU countries to provide biologically- tions at the receiving prealpine lakes range approximately from 200 m derived e-flows based on the requirements of the instream biota. How- asl (Lake Como and Lake Iseo) to 350 m asl (Lake Idro). Maximum runoff ever, the implementation of e-flows still remains a major issue in most is observed during late spring-early summer due to snowmelt. Flood of the EU countries. peaks can also occur in autumn, due to heavy rainfall. With the excep- Flow management in many Alpine streams is currently based on the tion of valley bottoms, the land is generally scarcely anthropized, with early e-flow approach focused on quantifying a single minimum flow prevailing activities related to mountain tourism; several areas of high (MF) sufficient to maintain aquatic species during crucial low-flow pe- naturalistic interest are also present. riods (Tennant, 1976). This approach however is based on historical hy- However, water resources in the area are massively exploited for hy- drological data series, without properly considering the requirements of dropower. Around 50 GW hydropower are currently installed in the en- the aquatic communities. E-flow recommendations based on simple hy- tire Alpine region (approximately 190,000 km2 area shared by eight drologic rules (McKay, 2015; Acreman, 2016)havebeenwidelyrecog- countries), providing renewable electricity of strategic importance on nized to be inadequate for sustaining the biological structures and the a European scale. In particular, peak-energy supply as well as grid- functionality of aquatic ecosystems (Poff et al., 1997). Current state-of- energy storage (i.e. pumped-storage hydroelectricity) is granted by Al- the-art approaches (e.g. Poff et al., 2010; Richter et al., 2012; Yin et al., pine reservoirs, providing about 12 km3 capacity overall (Permanent 2012; Yarnell et al., 2015) specifically advocate that flow recommenda- Secretariat of the Alpine Convention, 2009; Gaudard et al., 2014). The tions should be based on the mechanistic relationships between flows Italian Alps account for 28% of the Alpine region in terms of area. and ecological outcomes. Nevertheless, the limited availability of hydro- There, over 210 large reservoirs (e.g. storage N1Mm3 or dam height logical and ecological data for Alpine streams often prevents their appli- N 15 m) can store approximately 2.2 km3 of water. According to the cability (Vezza et al., 2012, 2014). available estimates concerning the five-year interval 2011–2015 Benthic macroinvertebrate monitoring is widely used to character- (Terna Rete Italia SpA, 2011, 2012, 2013, 2014, 2015), the overall hydro- ize river quality, also from a normative point of view, and also in the power capacity installed in the Italian Alps amounts to 15 GW, and is WFD framework (Birk and Hering, 2006). The impact of the streamflow mostly subdivided into 170 large plants (i.e. larger than 10 MW). The re- alteration on the biota has been frequently quantified through stream lated production exceeds 35 TWh per year, satisfying N10% of the Na- benthos sampling and analysis (e.g. Carlisle et al., 2014; Eddy et al., tional electricity demand. In the investigated catchments, hydropower 2017). Also in the Alpine environment, where streamflow alteration pervasivity is even greater: for instance, the overall installed power in can frequently be associated to hydropower, there are several studies the catchments of the Adda and Mera rivers above Lake Como (includ- available concerning stream quality assessment through benthos mon- ing the Swiss quota of the Mera basin) currently exceeds 2.4 GW, giving itoring (Bona et al., 2008; Brown et al., 2015). The specific subjects of an average productivity of approximately 6 TWh per year. Accordingly, these studies range from quality assessment at a regional level the ratio between installed power and catchment area (0.7 MW km−2) (Yoshimura et al., 2006), to analysis of invertebrate drift induced by is more than double than the Italian Alpine region (0.3 MW km−2). hydro/thermo-peaking (Bruno et al., 2010; Bruno et al., 2013), to resto- Hydropower development in the area dates back to the beginning of ration effects of artificial flooding in water depleted reaches below large the 1900′s, and, as it commonly occurs in the Alps, it is mostly per- reservoirs (Robinson et al., 2004; Robinson, 2012). However, current formed through complex “cascade” systems, where water abstraction water management based on MF release below water diversion struc- takes place at intakes of different size (Fig. 2 and Table S1 in the Supple- tures is surprisingly poorly investigated, both in terms of ecological re- mentary Material). In particular, according to the water storage avail- sponse and hydrological alteration. able at the withdrawal section, we have classified intakes with In this study, we present the results of a field investigation negligible storage, small reservoirs (e.g. available storage allows daily concerning the benthic macroinvertebrate response to the current to weekly regulation), reservoirs (available storage allows seasonal water management practices in the central Italian Alps, where strategi- regulation). cally important hydroelectricity at the National scale has longly been In order to obtain widespread exploitation of the available potential, generated. Hydrological and biological monitoring was carried out in the investigated catchments are overspread by several intakes (Fig. 1 twenty regulated stream reaches for five years. Since 2009, MFs have and Table S1), located both on the mainstem of the rivers and on the been implemented in the study area, ranging from 5 to 10% of the tributary streams of different order. As mentioned above, in order to mean annual natural flow estimated at the intake section. mitigate - at least partly - the impact of the off-stream diversion on